In a number of applications in the conveyor field, it has been found desirable to utilize two parallel propelling members to provide the driving force for moving the articles along the conveyor. In many specialized applications it has been found essential that the propelling member be of circular cross-section to reduce wear to an acceptable level and to solve the problem of maintaining proper tracking of the propelling members. Further, in certain type of applications, particularly where the rollers are skewed with respect to the principle axis of the conveyor, it has been found that only propelling members of circular cross-section can be utilized. To assure a high degree of fail-safe operation, it is considered desirable to utilize the propelling members in pairs so that the loss of one will not render the conveyor inoperative. When the propelling members are utilized in pairs, a serious problem has been encountered in maintaining proper support for the propelling members so that they exert reasonably identical bearing pressure against the conveyor rollers or against the articles to be conveyed. Also, provision must be made to assure adequate support pressure for the remaining propelling member when one of them breaks.